The methylenetetrahydrofolate reductase gene variant (C677T) in risk mothers with Down syndrome among Saudi population

Association of C677T and A1298C polymorphisms of the MTHFR gene with maternal risk for Down syndrome: A meta-analysis of case-control studies

BACKGROUND

Several studies around the world support the hypothesis that genetic polymorphisms involved in folate metabolism could be related to the maternal risk for Down syndrome (DS). Most of them investigated the role of MTHFR C677T and/or A1298C polymorphisms as maternal risk factors for DS, but their results are often conflicting and still inconclusive.

METHODS

We conducted a systematic review and meta-analysis to clarify the association of MTHFR C677T and/or A1298C polymorphisms with the maternal risk of DS. Our search strategy selected 42 eligible case control studies for a total of 4131 case mothers and 5452 control mothers. The Newcastle-Ottawa Scale was used to assess the methodological quality of the selected studies. To assess the confidence of statistically significant associations we applied false positive report probability test, and we performed the trial sequential analysis to minimize the type I error and random error.

RESULTS

We observed significant associations between the MTHFR C677T polymorphism and maternal risk for DS for each of the genetic models investigated (dominant, recessive, codominant, and allelic contrast). Subgroup analysis by region revelated significant association in the Asian population for all the genetic models investigated. Significant associations were also found for certain genetic models in North American, South American, and Middle Eastern populations, while no association was observed in Europeans. The MTHFR A1298C polymorphism did not show any association with the maternal risk of DS, either alone or in combination with the C677T one. The results of false positive report probability to verify the confidence of a significant association suggest that the association between the MTHFR C677T polymorphism and the maternal risk for DS is noteworthy, with high confidence in Asians.

CONCLUSION

The results of this meta-analysis support that the MTHFR C677T polymorphism, but not the A1298C one, is associated with the maternal risk for DS. Further studies are required to better characterize the contribution of gene-gene and gene-nutrient interactions as well as those of other regional or ethnic factors that could explain the observed different effect size in different populations.

Role of folate metabolizing genes and homocysteine in mothers of Down syndrome children

Objectives

Folates are essential nutrients required for the synthesis of DNA/RNA in cell division and segregation. Folates are reduced and methylated in the liver with the help of enzymes such as methylenetetrahydrofolate reductase (MTHFR), MTR MTRR, reduced folate carrier 1, and cystathionine-β-synthase. Variants in the genes encoding these enzymes may lead to hypomethylation, resulting in nondisjunction which in turn increases the risk for Down syndrome (DS). The present study was conducted to genotype these genes and to see their association with homocysteine levels.

Materials and Methods

A total of 213 mothers having DS children and 220 mothers having normal children were enrolled in the study. Genomic DNA was isolated from lymphocytes followed by polymerase chain reaction/Restriction Fragment Length Polymorphism for genotyping. Homocysteine levels were checked by chemoassay utilizing coumarin-based fluorescent probe.

Results

Genotypic frequency of MTHFR 1298 A > C polymorphism was significantly different among cases and controls (χ ² = 5.83, P = 0.01), presence of C instead of A allele provided protection against DS in mothers (odds ratios = 0.57, 95% confidence interval = 0.35-0.91, P = 0.01). Higher levels of homocysteine were independently associated with the risk of having DS child (P = 0.0001).

Conclusion

Homocysteine acted as an independent risk factor in the present study and was not associated with folate metabolizing gene variants.

An Assessment of Selected Molecular and Biochemical Markers of the Folate Pathway as Potential Risk Factors for Fetal Trisomy 21 during the First Trimester of Pregnancy in the Polish Population

Are the maternal gene variants MTHFR: c.665C>T, MTHFR: c.1286A>C, MTR: c.2756A>G, MTRR: c.66A>G, RFC1: c.80C>T and TCN2: c.776G>C and blood markers of the folate pathway important factors in assessing the risk of fetal trisomy 21 (fetal-T21)? Twenty pregnant women with a high risk and twenty with a low risk of fetal-T21 underwent prenatal examination. Selected gene variants and folate pathway markers and pregnancy-associated plasma protein A (PAPP-A) and free β-subunit of human chorionic gonadotropin β (free-β-hCG) multiple of the medians (MoMs) were determined. The distributions of the alternative alleles and genotypes of the gene variants did not differ between the studied groups. There was no relationship between PAPP-A and β-hCG MoM values and the presence of allele alternative genotype variants. The occurrence of alternative variants of the selected genes and concentrations of most of the studied folate pathway markers may not play a crucial role in the risk of fetal-T21 in pregnant women. However, the relationships between erythrocyte folate concentrations and the occurrence of alternative variants: c.665C>T MTHFR and c.776G>C TCN2, as well as the methylmalonic acid concentration and the occurrence of alternative variant c.776G>C TCN2 in pregnant women with fetal-T21, encourage further research. So far, of the biochemical markers, maternal PAPP-A and β-hCG MoM values remain independent risk factors for fetal-T21.

Maternal methylenetetrahydrofolate reductase C677T polymorphism and down syndrome risk: a meta-analysis from 34 studies

BACKGROUND

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme of folate metabolic pathway which catalyzes the irreversible conversion of 5, 10-methylenetetrahydrofolate to 5-methyltetrahydrofolate. 5-methyltetrahydrofolate donates methyl group for the methylation of homocysteine to methionine. Several studies have investigated maternal MTHFR C677T polymorphism as a risk factor for DS, but the results were controversial and inconclusive. To come into a conclusive estimate, authors performed a meta-analysis.

AIM

A meta-analysis of published case control studies was performed to investigate the association between maternal MTHFR C677T polymorphism and Down syndrome.

METHODS

PubMed, Google Scholar, Elsevier, Springer Link databases were searched to select the eligible case control studies using appropriate keywords. The pooled odds ratio (OR) with 95%confidence interval were calculated for risk assessment.

RESULTS

Thirty four studies with 3,098 DS case mothers and 4,852 control mothers were included in the present meta-analysis. The pooled OR was estimated under five genetic models and significant association was found between maternal MTHFR 677C>T polymorphism and Down syndrome under four genetic models except recessive model (for T vs. C, OR = 1.26, 95% CI = 1.09-1.46, p = 0.001; for TT vs. CC, OR = 1.49, 95% CI = 1.13-1.97, p = 0.008; for CT vs. CC, OR = 1.29, 95% CI = 1.10-1.51, p = 0.001; for TT+CT vs. CC, OR = 1.35, 95% CI = 1.13-1.60, p = 0.0008; for TT vs. CT+CC, OR = 0.76, 95% CI = 0.60-0.94, p = 0.01).

CONCLUSION

The results of the present meta-analysis support that maternal MTHFR C677T polymorphism is a risk factor for DS- affected pregnancy.